Adjust oven rack to middle position and preheat oven to 350 degrees. Spray a 13 by 9-inch casserole dish or baking pan with cooking spray and set aside.
Cut ¼ pound or 4 oz. Monterey Jack cheese, cheddar or Mexican blend into ½ inch cubes. On a separate plate, shred the remaining cheese (except the shredded Parmesan). Set aside.
Whisk flour, cornmeal, baking powder, salt, pepper, and cayenne in a large bowl.
Pulse half of corn and scallion whites in food processor until a coarse puree; about 12 pulses.
Stir pureed corn mixture into flour mixture.
Add sour cream, ¼ cup Parmesan, eggs, Jalapeños, if using, melted butter, remaining half of the corn, and cubed Monterey Jack.
Stir until combined. Transfer mixture to baking dish.
Smooth top so it's as level as possible.
Sprinkle with remaining ½ cup of grated Parmesan cheese. Then cover with Monterey Jack or whatever shredded cheese you're using. Use as much or as little as you like!
Bake until casserole is somewhat puffed up and cheese is a golden-brown color; between 45 to 50 minutes.
Transfer casserole to a wire rack and let cool for 10 minutes.
Sprinkle with green onions and fresh cilantro.
Serve and enjoy every bite.